1. Field of the Invention
The present invention relates to an image processing apparatus and an edge classification method.
2. Description of Related Art
Because a character and a line drawing are required to have a sharpness property, their edge parts are sometimes subjected to image processing different from that to the other regions. For example, edge enhancement processing is performed to an edge part, or screen processing is performed only to an edge part with a screen having a linear density different from those of the other regions. Moreover, it is sometimes judged whether an edge is an outer edge corresponding to a contour part or an inner edge situated on an inner part of the outer edge among the edges, and thereby different processing is performed to each of the outer edge and the inner edge. Alternatively, the signal values on the outer edge and the inner edge are sometimes operated, and thereby the balance between thinning and edge enhancement is attained.
Many judging methods of outer edges and inner edges have been proposed hitherto (see, for example, Japanese Patent Application Laid-open Publications Nos. 2000-307869 and 2005-176222). Japanese Patent Application Laid-Open Publication No. 2000-307869 discloses the method of judging the inside and the outside of an edge on the basis of brightness data, and Japanese Patent Application Laid-open Publication No. 2005-176222 discloses the method of performing edge enhancement before judging the inside and the outside of the edge on the basis of the positive and negative of the sign of the signal value.
In a printer or the like, an image is frequently saved once by being compressed and is expanded at the time of being printed. At this time, if the judgment of an edge is performed after expansion, then a line memory for holding an image and the processing circuit of the data become larger by the degree of the largeness of the data quantity of the image in comparison with that of the compressed data, and their costs become higher.
Also the case of being subjected to resolution conversion is similar. If an original image is subjected to resolution conversion to have lower resolution to be saved and is subjected to resolution conversion to that of the original image at the time of printing the image, then the cost of performing edge judgment in the state of high resolution becomes higher than that in the state of low resolution.